The number of Roman Catholics in Northern Virginia's outer suburbs is growing so fast that the local bishop has created a new parish and two new missions to serve more than 2,500 worshipers in Loudoun, Prince William, Culpeper and Rappahannock counties.

The missions will be carved from St. Stephen the Martyr Church in Middleburg, which has also been holding weekly services in South Riding and Bull Run since 2000 and refers to itself as "one parish -- three communities of faith."

The 1,000-member congregation that meets in Hutchinson Farm Elementary School in South Riding will become the Corpus Christi Mission. The 900 Catholics who meet at Bull Run Middle School in Prince William will become the St. Katherine Drexel Mission. St. Peter's mission in Washington, Va. -- the only Roman Catholic congregation in Rappahannock County -- will become a parish.

Missions are generally created in fast-growing areas that do not have enough worshipers to justify a parish, which has a lay leadership council that advises the priest, a permanent building and controls its own finances. Missions can be closed because of insufficient attendance or inadequate financial resources.

Church officials say the Diocese of Arlington, which includes 21 counties and seven cities in Northern Virginia, is one of the five fastest-growing dioceses in the United States, fueled by a large number of Hispanic and other immigrants and by workers attracted to dot-com and federal government jobs and more affordable housing in the outer suburbs. About 12,000 Catholics have been joining the diocese of about 400,000 each year.

Loudoun is the fastest-growing part of the diocese, with about 37,000 Catholics, followed by Prince William, which has roughly 47,000, said Richard Mullins, director of the diocese's multicultural ministries.

"It just keeps moving out and moving out," he said.

Mullins said about 25 percent of the residents in new subdivisions seek to affiliate with a local Roman Catholic church.

The growing congregations have prompted many Catholic churches in the region to offer Mass in new formats and different locations.

For about two years, St. Stephen in Middleburg has been holding Mass in Spanish on Sunday evenings, one of more than 30 such services in the diocese. Even with two English-language Masses on Sunday mornings and a Saturday afternoon vigil, the small-town church was not large enough to accommodate all the worshipers flocking to the area.

Church officials say that adding services at other locations can provide an immediate solution to the space crunch and provide worship opportunities closer to newly developed population centers.

On Sunday in South Riding, more than 250 people filled the school gym, taking up nearly all the chairs and filling most of the bleachers. The voices of the crowd, accompanied by a piano and an electric guitar, flowed through the room as a visiting priest stood behind a makeshift altar at center court. As worshipers made their way to receive Communion, the long lines wound around the gym.

Despite South Riding's burgeoning attendance, church officials estimate that dozens more Catholics who live in the Corpus Christi area worship instead at such established parishes as St. Timothy or St. Veronica, both in Chantilly.

"There's a lot of people moving into the area, and they expect their church to be present to them," said the Rev. Sean K. Rousseau, a priest at St. Stephen who has been appointed administrator of Corpus Christi.

Rousseau said about two dozen new families a month, most with young children, register for worship at South Riding, which now has services Saturday evenings and Sunday mornings. A third service, also Sunday mornings, will probably be added in September, Rousseau said, and about 400 students in kindergarten through 12th grade are expected to enroll in the mission's education programs for the upcoming school year.

Three services are held each Sunday in Bull Run in the school cafeteria. The Rev. William B. Schardt, the pastor at St. Ann in Arlington, will be the pastor at both St. Katharine Drexel and St. Stephen.

To become a parish, missions must obtain land for a church, maintain a stable attendance and become financially self-sufficient. For Corpus Christi and St. Katharine Drexel, the process could follow the path of St. Peter's, which began meeting in 1979 as an offshoot of Precious Blood in Culpeper. It has had its own church building since 1992 but lacked the status of parish until now.

"There's a greater sense of being united to the whole diocese by being a parish," said the Rev. Robert J. DeMartino, who has been the administrator of the St. Peter's congregation since 2003 and will now be its pastor. "There's an orphan mentality you can have if you're a mission."

The new missions were named in honor of the Year of the Eucharist that was proclaimed by the late Pope John Paul II and runs until October. Corpus Christi means the body of Christ in Latin. St. Katharine Drexel, a native of Philadelphia and the founder of the Sisters of the Blessed Sacrament, was canonized by John Paul II in 2000 and praised by him for her "spirituality based on prayerful union with the Eucharistic Lord."

The Corpus Christi Mission will serve southeastern Loudoun, including the Dulles District, which has seen a 66 percent growth in population from 2000 to 2003. The diocese said more than 4,000 Catholic families could live within the mission's boundaries by 2010.

The St. Katharine Drexel Mission will serve the rapidly growing suburban areas east of Bull Run Mountain, including the northern tip of Prince William County from the Loudoun and Fauquier county lines.

Diocese officials predict that more than 2,000 Catholic families could live within the mission's boundaries by 2010.

Catherine Bendskin reads announcements at Mass at Hutchinson Farm Elementary in South Riding on Sunday.

Michael Gorman, with his 7-month-old daughter, Audrey Clare, at Mass.